1. Field of the Invention
The present invention generally relates to reclamation of polyurethane elastomers and more particularly to the reclamation of cured polyurethane elastomers to form partially devulcanized elastomeric end products having improved properties.
2. Prior Art
A problem has existed relative to the disposal of scrap cured elastomers. To incinerate elastomers creates an air pollution problem because the combustion process causes toxic gases and photochemical compounds to be released. If, on the other hand, waste disposal is effected by burying the elastomers, not only is considerable expense involved but the buried material does not biodegrade. Moreover, cured elastomers are relatively expensive to produce so that waste disposal thereof constitutes a loss to the economy of potentially valuable material.
Accordingly, various methods have been proposed for the reclamation of different types of cured elastomeric materials. In this regard, it has been proposed to chemically treat elastomeric polyurethanes and the like either to isolate the same from impurities or to decompose the same to obtain reagents which can then be reacted to form useful products. In the former case, cured polyurethanes have been dissolved in various types of materials, such as amines, hexafluoroisopropanol, uncured polyurethanes and the like. In the latter case, polyurethanes have been heated to above their decomposition point to form decomposition liquids capable of reacting with di-isocyanates to produce useful products. As another example, polyurethanes have been heated in selected glycols to decompose the urethanes for isolation of useful reaction agents. As a third example, polyurethanes have been liquified in linear polyesters and polyester-amides in the presence of catalysts to dissociate the polyurethane linkages. Lower alcohol amines have also been used to peptize urethane linkages. Mixtures of amines, alkali metal hydroxides and oxides and the like have also been used for such purposes.
Attempts to recover a devulcanized or partially devulcanized and reusable form of polyurethane while preserving the polyurethane molecules have been largely unsuccessful. In most instances, it has been necessary to combine chemical dissolving or dissociating utilizing expensive, complicated, non-recoverable chemicals, along with physical methods including relatively high temperatures, resulting in degradation of physical characteristics of the products.
Accordingly, there is a need for a simple, inexpensive, rapid, efficient and reproducible method of breaking the cross-linkages of elastomeric cured polyurethanes without adversely affecting the molecular composition of the urethanes so as to provide materials which themselves form useful elastomeric products or which can be easily reacted to form useful materials. Preferably, such a method should not require expensive or complicated chemicals, difficult steps or specialized equipment and should not itself produce large amounts of pollutants.